Vibrating structures radiate sound. 
It might be tempting to reducing the radiation by reducing the vibrations on the plate (e.g. by make the structure stiffer). However, unfortunately, the efficiency of the radiation also depends on the vibration pattern on the structure, which might be changed when stiffening the structure.

In the animation a plate is mounted into an infinite, rigid wall (baffle).
Depending on the ratio between the wavelength on the plate and the wavelength in the surrounding media (e.g. air), the plate radiates with different efficiency. The size of the plate also influences the radiation efficiency.

Keywords:

        monopole
        dipole
        quadrupole
        near field
        hydrodynamic short-circuiting
        radiation efficiency
 
